Granular phorate (0,0-diethyl S-(ethylthio)methyl phosphorodithioate) was applied to the soil surface around the bole of 7-yr-old Douglas-firs (Pseudotsuga menziesii (Mirb.) Franco) at 1 g active ingredient (AI)/tree. Needles, bark, xylem, new growth composites, and treated soil were assayed for the insecticide and its metabolites by gas chromatography and thin-layer chromatography at intervals over a 17-month period. Phorate metabolites were translocated to aerial parts and were recovered from bark and needles throughout the entire period. Phorate sulfoxide (PSO) and phorate sulfone (PSO2 were the only compounds found in significant quantifies. Neither phorate nor its oxygen analogue was detected. The ratio of PSO2 to PSO increased with time and was greater in bark than in needles. In soil, phorate was rapidly oxidized to PSO and PSO2 Phorate remained in the upper 2.5 cm of soil, but PSO and PSO2 leached downward with the largest concentrations occurring in the 5- to 10-cm zone. FOREST SCI. 23:355-360.

Affiliations:
Former Associate Entomologist, Western Washington Research and Extension Center, Washington State University, Puyallup, WA 98371

Publication date: 1977-09-01

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